Poly(amidoamine) hyperbranched systems: synthesis, structure and characterization

Abstract

Hyperbranched analogues of the Tomalia PAMAM dendrimer system have been prepared from a series of AB 2 aminoacrylate hydrochloride monomers using Michael addition chemistry, where A represents a Michael acceptor and B 2 a primary aliphatic amine. This step-growth polymerization process has led to the synthesis of poly(amidoamine) hyperbranched materials, examples of which exhibit a branching factor close to one. This degree of branching, calculated from quantitative 15N NMR spectroscopy data, is consistent with other spectroscopic characterization undertaken and the assignment of the 15N NMR shifts observed correlates well with the available literature data. The use of MALDI-TOF mass spectrometry as a tool to evaluate the possibility of intramolecular cyclization reactions between the focus and terminal groups is discussed along with the determination of molecular weights and molecular weight distributions for these amidoamine hyperbranched polymers. The synthesis of pseudo-dendrimers through `one-pot' AB 2/B n copolymerizations, where control over both molecular weight and extent of branching through the B n unit is illustrated. A poly(amidoamine) hyperbranched AB 2/B 6 copolymer is shown to display a viscosity/molecular weight profile similar to that exhibited by dendrimers. The effect of varying the internal spacer unit length between the branch points A and B is discussed, with reference to both the standard AB 2 polymerizations and the core terminated AB 2/B n copolymerizations. Preliminary physical characterisation ( T g, DSC and solution viscosity) of these novel materials is reported.